Relief images can be provided and used in various articles for many different purposes. For example, the electronics, display, and energy industries rely on the formation of coatings and patterns of conductive materials to form circuits on organic and inorganic substrates. Such coatings and patterns are often provided using relief imaging methods and relief image forming elements. There is also need for means to provide fine wiring in various articles.
Microelectronic devices have been prepared by photolithographic processes to form necessary patterns. Photolithography, however, is a complex, multi-step process that is too costly for the printing of electronic devices on plastic substances.
Contact printing is a flexible, non-lithographic method for forming patterned materials. Contact printing potentially provides a significant advance over conventional photolithographic techniques since contact printing can form relatively high resolution patterns for electronic parts assembly. Microcontact printing can be characterized as a high resolution technique that enables patterns of micrometer dimensions to be imparted onto a substrate surface. Contact printing is a possible replacement to photolithography in the fabrication of microelectronic devices, such as radio frequency tags (RFID), sensors, and memory and back panel displays. The capability of microcontact printing to transfer a self-assembled monolayer (SAM) forming molecular species to a substrate has also found application in patterned electroless deposition of metals. SAM printing is capable of creating high resolution patterns, but is generally limited to forming metal patterns of gold or silver for example using thiol chemistry. Although there are variations, in SAM printing a positive relief pattern provided on an element having a relief image is inked onto a substrate.
Flexography is a one method of printing or pattern formation that is commonly used for high-volume printing runs. It is usually employed for printing on a variety of soft or easily deformed materials including but not limited to, paper, paperboard stock, corrugated board, polymeric films, fabrics, metal foils, glass, glass-coated materials, flexible glass materials, and laminates of multiple materials. Coarse surfaces and stretchable polymeric films are economically printed using flexography.
Flexographic printing members are sometimes known as “relief” printing members (for example, relief-containing printing plates, printing sleeves, or printing cylinders) and are provided with raised relief images onto which ink is applied for application to a printable material. While the raised relief images are inked, the relief “floor” should remain free of ink. These flexographic printing precursors are generally supplied with one or more imageable layers that can be disposed over a backing layer or substrate. Flexographic printing also can be carried out using a flexographic printing cylinder or seamless sleeve having the desired relief image.
A method for printing with a conductive ink using a relief printing plate at high print speed is described in U.S. Patent Application Publication 2004/0003734 (Shively et al.).
U.S. Pat. No. 7,026,012 (Chen et al.) describes a method for transferring catalytic particles from a stamp to a substrate followed by plating the catalytic particles.
U.S. Patent Application Publication 2008/0233280 (Blanchet et al.) describes the use of an elastomeric stamp having a relief structure with a raised surface that is treated with heat or by other means to enhance its wettability, and then application and transfer of a functional material to form a pattern on a substrate.
While there are numerous methods described in the art to form patterns using relief images, there remains a need to find a way to consistently provide patterns with high resolution lines (for example, 10 μm or less) and feature uniformity using various printable material compositions (or what are sometimes known as “inks”). The industry has been pursuing these goals for many years with limited success and continued research is being done to achieve these goals using a wide variety of print materials. A number of problems must been addressed to achieve the desired high resolution lines.
U.S. Pat. No. 6,772,683 (Laksin et al.) describes a method for applying sequential the same flexographic printing ink by controlling the time between ink layer applications such that sufficient diluents evaporates from each applied layer to increase the viscosity of the first applied layer. A similar method is also described in U.S. Patent Application Publication 2007/0289459 (Laksin et al.) in which sequentially applied ink layers are partially cured.
U.S. Pat. No. 7,026,012 (Chen et al.) describes multiple depositing the same composition of catalytic particles on a selected area of a stamp for eventual application to a substrate.
Transfer of silver-containing conductive “inks” using the noted flexographic printing processes relies upon a good release of the conductive ink from the elastomeric relief element in contact with a receiver element, good affinity of the conductive ink for the receiver element, and the compositional cohesiveness of the conductive ink. There are continued efforts to solve these problems and especially to improve the internal cohesiveness as well as the conductivity of the conductive materials in the transferred ink.
There are numerous structures that can, in theory, be printed. One difficulty with printing multilayer structures, especially to achieve fine features (such as fine lines), is accurate alignment of repeated printing steps. When printing metallic lines, there is also a problem that many conductive inks are highly reflective, and this reflectivity can be a concern in multilayer structures for certain uses, such as transparent conductive elements.
The present invention is one effort to address one or more of these problems and to provide an improved method for printing a conductive relief image particularly using electrically conductive compositions.